Seinäjoki is a city located in Southern Ostrobothnia, Finland. Seinäjoki originated around the Östermyra bruk iron and gunpowder factories founded in 1798. Seinäjoki became a municipality in 1868, köping in 1931 and town in 1960. In May 2007 it was agreed that the smaller neighbouring municipalities of Nurmo and Ylistaro will merge with Seinajoki in 2009 to form Greater Seinäjoki.
The Town library, Lakeuden Risti church and central administrative buildings are designed by Alvar Aalto.
Seinäjoki is known for hosting two large summer events: Tangomarkkinat, which is a tango festival attracting more than 100,000 visitors annually, and Provinssirock, which is the biggest rock festival in Finland.
The asteroid 1521 Seinäjoki bears its name.
Seinäjoki was historically called Östermyra in Swedish. Today, this name is very seldomly used even by those who are Swedish-speaking.

• the cross of the plains
  
• Alvar Aalto's cultural and administrative centre
  
• the Southern Ostrobothnia District Museum
  
• the Civil Guard and Lotta Svärd museum
  
• Törnävä church
  
• the railway exhibition
  
  Other points of interest
  
• Törnävä tourist centre
  
• the Suviyö trotting-race
  
• the summer theatre
  
• the Jouppilanvuori winter sports centre
  
• the Seinäjoki City theatre
  
• the traffic centre with six roads and five railway junctions
  
• Provinssirock
  
• Tangomarkkinat
  
• Vauhtiajot